A conventional hermetic compressor contains a certain amount of lubricating oil inside a hermetic container instead of supplying the oil forcibly from the outside of the compressor for the reason of its structural hurdles. Therefore, refrigerant containing the lubricating oil circulates through a refrigeration system and returns to a refrigerant inflow side of the compressor even if the oil is discharged with the refrigerant from the hermetic container. The structure constructed as above thus maintains the certain amount of oil at all the time and keeps lubrication of the compressing mechanism.
In the conventional hermetic compressor of this kind, however, there is a possibility of running short of an amount of returning oil depending on its operating condition, and this can cause a deficiency of lubrication. As one of measures for the above problem, therefore, temperature detecting devices are disposed to portions of the hermetic container, one in the oil and another in the gas above the oil surface, to take signals representing their temperatures, and to detect a level of the oil surface based on a difference between the two detected temperatures. The measures contrived here is to control an operating condition of the compressor according to the detected result in a manner to constantly maintain a proper amount of the oil retained therein. One example of such contrivances is disclosed in Japanese Patent Unexamined Publication, No. 2001-032772.
However, the above-described structure of the prior art requires not only two or more temperature detecting devices but also insulation terminals for mounting these temperature detecting devices individually to the hermetic container. There is hence a problem that the structure is complex and detection of accurate temperatures is difficult due to spatial limitation for mounting locations of the temperature detecting devices.